Arto Laine

Peripheral neuropathy and vibration syndrome

SummaryHundred and three patients with suspected or diagnosed vibration syndrome caused by the prolonged use of chain saws were examined during 1978–1980. Neurological or neurophysiological examinations revealed slight changes suggesting polyneuropathy in the lower extremities of 42 patients. Peripheral neuropathy in the upper extremities was only detected in 39 patients. No evidence of peripheral neuropathy was found for 22 patients. The polyneuropathic patients did not significantly differ from the non-polyneuropathic patients with regard to other clinical symptoms and signs, laboratory findings, or data on exposure. We concluded that patients with neuropathic diathesis tend to be selected into groups of patients with suspected vibration syndrome. This study emphasizes the need for the careful neurological examination of each patient with suspected vibration syndrome.

Immediate effects of m-xylene on the human central nervous system.

Male volunteers were exposed to m-xylene vapour for 4 h a day either sedentary or with a period of 10 min exercise twice a day with stable (8.2 mumol/l) m-xylene concentrations or fluctuating concentrations with peaks (16.4 mumol/l). The TWA concentration was always the same (8.2 mumol/l). The body balance of the subjects was clearly impaired in the anteroposterior (a-p) direction, especially with their eyes closed during the peaks at rest, whereas it was improved when exercise was included in spite of the higher blood m-xylene concentrations. When on the contrary, the situation was reversed in the lateral direction. Complex audiomotor reactions were impaired after the peaks combined with exercise, whereas changes in simple reaction times were similar in pattern to those found for body balance in the a-p direction. The results suggest a complex interaction between physiological factors and m-xylene and development of adaptation or tolerance during the exposure.

Changes induced by short-term xylene exposure in human evoked potentials

SummaryNine healthy male volunteers were exposed to m-xylene for 3 h in the morning and 40 min in the afternoon with a 40-min break in between. The atmospheric m-xylene concentrations were either stable at 8.2 μmol/l (200 ppm) or they fluctuated (5.2–16.4 μmol/1; 135–400 ppm) with peaks of 16.4 μmol/1 and duration of 20 min at the beginning of each exposure session. The subjects were either sedentary or exercised at 100 W for 10 min at the beginning of each session during both exposure types. The two control days, with and without exercise, were similar to the exposure days but without exposure. Evoked potentials were recorded in the morning before the exposure and immediately after the morning and afternoon sessions. Visual evoked potentials were studied to a pattern reversal stimulus (pattern VEP) and to a light flash (flash VEP). For pattern VEPs the latencies of P50, N70, P100, N135 and P170 as well as the peak-to-peak amplitude of N70 to P100 were measured. For flash VEPs the latencies of P50, N70, P100, N150 and P200 as well as the peak-to-peak amplitude of P100 to N150 were measured. Short-latency auditory evoked potentials arising in the brainstem (BAEP) were recorded for a click stimulus. The peaks 1, II, III, IV and V were identified from the grand averages. The effect of various exposure paradigms was evaluated by comparing the individual changes on an exposure day to those during the control days. The latency N135 of the pattern VEP decreased in exposure at 400 ppm with exercise, and the latency P210 in the flash VEP decreased both at the stable and fluctuating exposure with exercise. The results might suggest some activation of the arousal level of the subjects after the most intensive exposure situations.

ELECTROENCEPHALOGRAPHIC FINDINGS DURING EXPERIMENTAL HUMAN EXPOSURE TO M-XYLENE

Aromatic hydrocarbon solvents, used widely in industry, cause central nervous system symptoms in exposed workers. Acute effects of m-xylene were studied in nine voluntary subjects exposed experimentally to stable or varying concentrations of m-xylene at rest or while exercising. Each subject participated in four exposure and two control sessions in a single-blind fashion. The time-weighted average (TWA) m-xylene concentration was always 200 parts per million (ppm) (8.2 mumol/l) during the 4-h exposure period, complying to a TWA of 4.1 mumol/l.8 h, which is equivalent to the hygienic limit allowed in work situations. The short-term peak concentrations were 400 ppm or less. Electroencephalography was recorded at the beginning of exposure, during exposure, and after exposure was stopped. Eighteen 60-s EEG samples for each subject on each experimental day were analyzed automatically. Exercise increased theta percentage and delta power and percentage; these changes were more prominent in the control session without exposure. Exposure increased the dominant alpha frequency and alpha percentage during the early phase of exposure and also counteracted the effects of exercise. The effects of short-term m-xylene exposure on EEG were minor, and no deleterious effects were noted. Perhaps alpha activation is indicative of stimulating and excitatory effects induced by m-xylene exposure, which has been noted heretofore in the absorption phase of alcohol intake.

Acute effects of 1,1,1-trichloroethane inhalation on the human central nervous system

The object of this study was to examine the immediate nervous effects of variable 1,1,1-trichloroethane (TCE) exposure combined with physical exercise. The effects on the quantitative electroencephalography (EEG), visual evoked potentials (VEP) and body sway were analyzed. Nine male volunteers were exposed to either a stable or a fluctuating exposure pattern with the same time-weighted average concentration of 200 ppm (8.1 μmol/l). In both cases, the subjects engaged in physical exercise during the exposures. Exercise alone induced an increase in the dominant alpha frequency in the EEG and, after an initial drop, an increase in the alpha percentage with a concomitant decrease in theta, whereas delta and beta bands remained unaffected. By contrast, exposure to TCE and exercise did not affect the alpha, theta or delta activities but induced changes in beta during the morning recordings at peak exposure to TCE. The body sway tended to decrease slightly during the fluctuating TCE exposure, and the later peaks in VEPs showed slight prolongations. Overall, no deleterious effects of exposure were noted.

Acute effects of m-xylene inhalation on body sway, reaction times, and sleep in man.

SummaryNine male volunteers were exposed to either a constant or a fluctuating exposure pattern of m-xylene with a time-weighted average exposure concentration of 200 ppm in both cases. The subjects remained sedentary throughout the exposure, or the exercised at 100W for 10 min at the beginning of the morning and the afternoon sessions. In another experiment, 12 sedentary male volunteers were exposed to a fixed 200 ppm of m-xylene. The effects of m-xylene on body sway, reaction time performance, and overnight sleep were measured. Body balance was stabilized after exposure to the peaks of 400 ppm of m-xylene in both sedentary and exercising subjects. Simple visual reaction times were prolonged after the peak exposures at rest whereas auditive choise reaction times were prolonged after peaks combined with exercise. Exposure to m-xylene at a constant level of 200 ppm did not affect the ratio of “active” to “quite” sleep in the volunteers as measured with the static charge sensitive bed recording, but decreased slightly the number of body movements in bed. On the next morning no changes were found in body sway and reaction time performance as compared to the morning before exposure.

Short-Term Exposure of Human Subjects to m-Xylene and 1,1,1-Trichloroethane

Inhalation exposure of male volunteers to m-xylene (8.2 mumol/l, 200 ppm) and 1,1,1-trichloroethane (TCE) (8.2 and 16.4 mumol/l, 200 and 400 ppm), as well as to a combination of TCE (16.4 mumol/l) and xylene (8.2 mumol/l), induced only slight changes in psychophysiological functions such as body sway and reaction time. Exposure to the 8.2 mumol/l concentration of xylene or TCE tended to improve the performances, whereas TCE exposure at 16.4 mumol/l alone or in combination with xylene tended to have an opposite effect. The results thus suggest a biphasic acute effect of TCE on the central nervous system (CNS) and reveal that xylene and TCE together exhibit neither kinetic interaction nor synergistic nor antagonistic acute effects on the CNS functions studied.